The invention relates to a supertwist liquid crystal display with
two plane-parallel carrier plates which, with a bordering, form a cell, PA1 a nematic liquid crystal mixture, located in the cell, having a positive dielectric anisotropy and at least one chiral doping material, PA1 electrode layers with superposed orientation layers on the insides of the carrier plates, PA1 a tilt angle of about 1.degree. to 30.degree. between the longitudinal axis of the molecules at the surface of the carrier plates and the carrier plates, and PA1 a twist angle of the liquid crystal mixture in the cell from orientation layer to orientation layer of an amount between 160.degree. and 450.degree., PA1 a nematic phase range of at least 60.degree. C., PA1 a viscosity of 30 mPa.s or lower, and PA1 .DELTA..epsilon./.epsilon..perp.&lt;2.0, where .DELTA..epsilon. is the dielectric anisotropy and .epsilon..perp. is the dielectric constant in the direction of the short axis of the liquid crystal molecule. PA1 a nematic phase range of at least 60.degree. C., PA1 a viscosity of 30 mPa.s or lower, and PA1 .DELTA..epsilon./.epsilon..perp.&lt;2.0, where .DELTA..epsilon. is the dielectric anisotropy and .epsilon..perp. is the dielectric constant in the direction of the short axis of the liquid crystal molecules. PA1 two plane-parallel carrier plates which, with a bordering, form a cell, PA1 a nematic liquid crystal mixture, located in the cell, having a positive dielectric anisotropy and at least one chiral doping material, PA1 electrode layers with superposed orientation layers on the insides of the carrier plates, PA1 a tilt angle of about 1.degree. to 30.degree. between the longitudinal axis of the molecules at the surface of the carrier plates and the carrier plates, and PA1 a twist angle of the liquid crystal mixture in the cell from orientation layer to orientation layer of an amount between 160.degree. and 450.degree., PA1 a nematic phase range of at least 60.degree. C., PA1 a viscosity of 30 mPa.s or lower, and PA1 .DELTA..epsilon./.epsilon..perp.&lt;2.0, where .DELTA..epsilon. is the dielectric anisotropy and .epsilon..perp. is the dielectric constant in the direction of the short axis of the liquid crystal molecules. PA1 the product of the birefringence .DELTA.n and the layer thickness of the liquid crystal mixture is between 0.1 .mu.m and 2.5 .mu.m, PA1 the dielectric constant .epsilon..perp. is greater than or equal to 4, preferably greater than or equal to 5, PA1 the dielectric anisotropy .DELTA..epsilon. is greater than or equal to 5, PA1 the liquid crystal mixture contains at least one 1,4-disubstituted 2,3-difluorobenzene compound, PA1 the 2,3-difluorobenzene compound contains a 4-substituted 2,3-difluorophenoxy group, PA1 the 2,3-difluorobenzene compound is a compound of the formula I ##STR1## wherein R.sup.1 and R.sup.2 each independently of one another are alkyl having 1 to 15 C atoms or alkenyl having 3 to 15 C atoms, it also being possible for one CH.sub.2 group in each of these radicals to be replaced by --O--, --CO--, --CO--O-- or --O--CO--, and one of the radicals R.sup.1 and R.sup.2 can also be F, Cl, CN, NCS, CF.sub.3 or OCF.sub.3, PA1 the liquid crystal mixture contains at least one liquid-crystalline compound with the structural element ##STR2## wherein Q.sup.1 and Q.sup.2 independently of one another are trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene or 2,3-difluoro-1,4-phenylene, PA1 the liquid crystal mixture contains at least one compound of the following formulae A to G: ##STR3## wherein R.sup.A and R.sup.B each independently of one another are alkyl having 1 to 15 C atoms or alkenyl having 3 to 15 C atoms, it also being possible for one CH.sub.2 group in each of these radicals to be replaced by --O--, --CO--, --CO--O-- or --O--CO--, the liquid crystal mixture contains at least one compound of the following formulae H to K: ##STR4## wherein n is 1 or 2 and, in the case of n=2, the two fluorine atoms are adjacent, and R.sup.A and R.sup.B have the meaning given above, PA1 the liquid crystal mixture contains at least one liquid-crystalline tolane compound with the structural element ##STR5## wherein Q.sup.1 and Q.sup.2 independently of one another are 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene or 2,3-difluoro-1,4-phenylene, PA1 the liquid crystal mixture contains at least one compound of the following formulae L to Q: ##STR6## wherein R.sup.A and R.sup.B each independently of one another are alkyl having 1 to 15 C atoms or alkenyl having 3 to 15 C atoms, it also being possible for one CH.sub.2 group in each of these radicals to be replaced by --O--, --CO--, --CO--O-- or --O--CO--, PA1 the liquid crystal mixture contains at least one compound of the following formulae R and/or S: ##STR7## wherein R.sup.C and R.sup.D each independently of one another are n-alkyl having 1 to 10 C atoms or (trans)-n-alkenyl having 3 to 10 C atoms, PA1 the liquid crystal mixture contains an ethyne compound of the formula II ##STR8## wherein R.sup.1 and R.sup.2 each independently of one another are alkyl having 1 to 15 C atoms or alkenyl having 3 to 15 C atoms, it also being possible for one CH.sub.2 group in each of these radicals to be replaced by --O--, --CO--, --CO--O-- or --O--CO--, and one of the radicals R.sup.1 and R.sup.2 can also be F, Cl, CN, NCS, CF.sub.3 or OCF.sub.3, PA1 the liquid crystal mixture contains at least one liquid-crystalline compound with the structural element ##STR9## wherein Q.sup.3 is trans-1,4-cyclohexylene, 1,4-phenylene, 2-fluoro-1,4-phenylene, 3-fluoro-1,4-phenylene or 2,3-difluoro-1,4-phenylene, PA1 the liquid crystal mixture contains at least one compound of the following formulae E1 to E7: ##STR10## wherein each R.sup.E is an n-alkyl having 1 to 10 C atoms or (trans)-n-alkenyl having 3 to 10 C atoms, R.sup.F is n-alkyl having 1 to 10 C atoms, n-alkoxy having 1 to 10 C atoms, (trans)-n-alkenyl having 3 to 10 C atoms, F or CN, and X and Y each independently of one another are H or F, the liquid crystal mixture contains at least one compound of the formulae E3 to E7, PA1 the liquid crystal mixture contains at least one compound of the formulae E3 to E7, wherein R.sup.F is n-alkyl or n-alkenyl and X and Y are each H, PA1 the liquid crystal mixture contains at least one compound of the formulae E3 to E7, wherein R.sup.F is fluorine, X is H and Y is H or fluorine, PA1 the liquid crystal mixture contains at least one compound of the formulae E3 to E7, wherein R.sup.F is cyano. PA1 a nematic phase range of at least 60.degree. C., PA1 a viscosity of 30 mPa.s or lower, and PA1 .DELTA..epsilon./.epsilon..perp.&lt;2.0, where .DELTA..epsilon. is the dielectric anisotropy and .epsilon..perp. is the dielectric constant in the direction of the short axis of the liquid crystal molecules, as the dielectrics of SLC displays.
characterized in that the nematic liquid crystal mixture satisfies the following conditions:
Supertwist liquid crystal displays (SLC displays) according to the preamble are known, for example from EP 0,131,216 B1; DE 3,423,993 A1; EP 0,098,070 A2; M. Schadt and F. Leenhouts, 17th Freiburger Arbeitstagung Flussigkristalle [Freiburg Working Meeting on Liquid Crystals] (8.-10.04.87); K. Kawasaki et al., SID 87 Digest 391 (20.6); M. Schadt and F. Leenhouts, SID 87 Digest 372 (20.1); K. Katoh et al., Japanese Journal of Applied Physics, volume 26, No. 11, L 1784-L-1786 (1987); F. Leenhouts et al., Appl. Phys. Lett. 50 (21), 1468 (1987); H. A. van Sprang and H. G. Koopman, J. Appl. Phys. 62 (5), 1734 (1987); T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (10), 1021 (1984), M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (5), 236 (1987) and E. P. Raynes, Mol. Cryst. Liq. Cryst. Letters volume 4 (1), pages 1-8 (1986). The term SLC display here comprises any more highly twisted display with an amount of twist angle between 160.degree. and 360.degree., such as, for example, the displays according to Waters et al. (C. M. Waters et al., Proc. Soc. Inf. Disp. (New York) (1985) (3rd Intern. Display Conference, Kobe, Japan), the STN-LCD's (German Offenlegungsschrift 3,503,259), SBE-LCD's (T. J. Scheffer and J. Nehring, Appl. Phys. Lett. 45 (1984) 1021), OMI-LCD's (M. Schadt and F. Leenhouts, Appl. Phys. Lett. 50 (1987), 236, DST-LCD's (European Published Application 0,246,842) or BW-STN-LCD's (K. Kawasaki et al., SID 87 Digest 391 (20.6)).
Compared with standard twisted nematic displays, displays of this type are distinguished by substantially better steepness of the electro-optical characteristic and thus associated better contrast values and by a substantially smaller angle dependence of the contrast. Supertwist displays with a very high steepness of the characteristic are here of particular interest. The measure taken for the steepness of the characteristic is in general the ratio V.sub.50 /V.sub.10 (V.sub.50 =voltage at 50% contrast/V.sub.10 =voltage at 10% contrast). To achieve high steepnesses of the characteristics, especially the elastic properties of the liquid crystal mixture have hitherto been optimized. However, the steepnesses achieved were not adequate for some applications.